2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
26 #include "ucioption.h"
28 using namespace Search;
30 ThreadPool Threads; // Global object
32 namespace { extern "C" {
34 // start_routine() is the C function which is called when a new thread
35 // is launched. It is a wrapper to the virtual function idle_loop().
37 long start_routine(Thread* th) { th->idle_loop(); return 0; }
42 // Thread c'tor starts a newly-created thread of execution that will call
43 // the the virtual function idle_loop(), going immediately to sleep.
45 Thread::Thread() : splitPoints() {
47 is_searching = do_exit = false;
48 maxPly = splitPointsCnt = 0;
52 if (!thread_create(handle, start_routine, this))
54 std::cerr << "Failed to create thread number " << idx << std::endl;
60 // Thread d'tor waits for thread termination before to return
64 do_exit = true; // Search must be already finished
66 thread_join(handle); // Wait for thread termination
70 // TimerThread::idle_loop() is where the timer thread waits msec milliseconds
71 // and then calls check_time(). If msec is 0 thread sleeps until is woken up.
72 extern void check_time();
74 void TimerThread::idle_loop() {
79 do sleepCondition.wait_for(mutex, msec ? msec : INT_MAX);
80 while (!msec && !do_exit); // Don't allow wakeups when msec = 0
88 // MainThread::idle_loop() is where the main thread is parked waiting to be started
89 // when there is a new search. Main thread will launch all the slave threads.
91 void MainThread::idle_loop() {
97 is_finished = true; // Always return to sleep after a search
100 while (is_finished && !do_exit)
102 Threads.sleepCondition.notify_one(); // Wake up UI thread if needed
103 sleepCondition.wait(mutex);
115 assert(is_searching);
120 // Thread::notify_one() wakes up the thread, normally at split time
122 void Thread::notify_one() {
125 sleepCondition.notify_one();
130 // Thread::wait_for() set the thread to sleep until condition 'b' turns true
132 void Thread::wait_for(volatile const bool& b) {
135 while (!b) sleepCondition.wait(mutex);
140 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
141 // current active split point, or in some ancestor of the split point.
143 bool Thread::cutoff_occurred() const {
145 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
153 // Thread::is_available_to() checks whether the thread is available to help the
154 // thread 'master' at a split point. An obvious requirement is that thread must
155 // be idle. With more than two threads, this is not sufficient: If the thread is
156 // the master of some active split point, it is only available as a slave to the
157 // slaves which are busy searching the split point at the top of slaves split
158 // point stack (the "helpful master concept" in YBWC terminology).
160 bool Thread::is_available_to(Thread* master) const {
165 // Make a local copy to be sure doesn't become zero under our feet while
166 // testing next condition and so leading to an out of bound access.
167 int spCnt = splitPointsCnt;
169 // No active split points means that the thread is available as a slave for any
170 // other thread otherwise apply the "helpful master" concept if possible.
171 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master->idx));
175 // init() is called at startup. Initializes lock and condition variable and
176 // launches requested threads sending them immediately to sleep. We cannot use
177 // a c'tor becuase Threads is a static object and we need a fully initialized
178 // engine at this point due to allocation of endgames in Thread c'tor.
180 void ThreadPool::init() {
182 sleepWhileIdle = true;
183 timer = new TimerThread();
184 threads.push_back(new MainThread());
189 // exit() cleanly terminates the threads before the program exits.
191 void ThreadPool::exit() {
193 delete timer; // As first becuase check_time() accesses threads data
195 for (size_t i = 0; i < threads.size(); i++)
200 // read_uci_options() updates internal threads parameters from the corresponding
201 // UCI options and creates/destroys threads to match the requested number. Thread
202 // objects are dynamically allocated to avoid creating in advance all possible
203 // threads, with included pawns and material tables, if only few are used.
205 void ThreadPool::read_uci_options() {
207 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
208 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
209 size_t requested = Options["Threads"];
211 assert(requested > 0);
213 while (threads.size() < requested)
214 threads.push_back(new Thread());
216 while (threads.size() > requested)
218 delete threads.back();
224 // available_slave_exists() tries to find an idle thread which is available as
225 // a slave for the thread 'master'.
227 bool ThreadPool::available_slave_exists(Thread* master) const {
229 for (size_t i = 0; i < threads.size(); i++)
230 if (threads[i]->is_available_to(master))
237 // split() does the actual work of distributing the work at a node between
238 // several available threads. If it does not succeed in splitting the node
239 // (because no idle threads are available, or because we have no unused split
240 // point objects), the function immediately returns. If splitting is possible, a
241 // SplitPoint object is initialized with all the data that must be copied to the
242 // helper threads and then helper threads are told that they have been assigned
243 // work. This will cause them to instantly leave their idle loops and call
244 // search(). When all threads have returned from search() then split() returns.
247 Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
248 Value bestValue, Move* bestMove, Depth depth, Move threatMove,
249 int moveCount, MovePicker& mp, int nodeType) {
251 assert(pos.pos_is_ok());
252 assert(bestValue > -VALUE_INFINITE);
253 assert(bestValue <= alpha);
254 assert(alpha < beta);
255 assert(beta <= VALUE_INFINITE);
256 assert(depth > DEPTH_ZERO);
258 Thread* master = pos.this_thread();
260 if (master->splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
263 // Pick the next available split point from the split point stack
264 SplitPoint& sp = master->splitPoints[master->splitPointsCnt];
266 sp.parent = master->curSplitPoint;
269 sp.slavesMask = 1ULL << master->idx;
271 sp.bestMove = *bestMove;
272 sp.threatMove = threatMove;
275 sp.nodeType = nodeType;
276 sp.bestValue = bestValue;
278 sp.moveCount = moveCount;
283 assert(master->is_searching);
285 master->curSplitPoint = &sp;
288 // Try to allocate available threads and ask them to start searching setting
289 // is_searching flag. This must be done under lock protection to avoid concurrent
290 // allocation of the same slave by another master.
294 for (size_t i = 0; i < threads.size() && !Fake; ++i)
295 if (threads[i]->is_available_to(master))
297 sp.slavesMask |= 1ULL << i;
298 threads[i]->curSplitPoint = &sp;
299 threads[i]->is_searching = true; // Slave leaves idle_loop()
300 threads[i]->notify_one(); // Could be sleeping
302 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
306 master->splitPointsCnt++;
311 // Everything is set up. The master thread enters the idle loop, from which
312 // it will instantly launch a search, because its is_searching flag is set.
313 // The thread will return from the idle loop when all slaves have finished
314 // their work at this split point.
315 if (slavesCnt || Fake)
317 master->Thread::idle_loop(); // Force a call to base class idle_loop()
319 // In helpful master concept a master can help only a sub-tree of its split
320 // point, and because here is all finished is not possible master is booked.
321 assert(!master->is_searching);
324 // We have returned from the idle loop, which means that all threads are
325 // finished. Note that setting is_searching and decreasing splitPointsCnt is
326 // done under lock protection to avoid a race with Thread::is_available_to().
330 master->is_searching = true;
331 master->splitPointsCnt--;
332 master->curSplitPoint = sp.parent;
333 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
334 *bestMove = sp.bestMove;
342 // Explicit template instantiations
343 template Value ThreadPool::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
344 template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
347 // wait_for_search_finished() waits for main thread to go to sleep, this means
348 // search is finished. Then returns.
350 void ThreadPool::wait_for_search_finished() {
352 MainThread* t = main_thread();
354 while (!t->is_finished) sleepCondition.wait(t->mutex);
359 // start_searching() wakes up the main thread sleeping in main_loop() so to start
360 // a new search, then returns immediately.
362 void ThreadPool::start_searching(const Position& pos, const LimitsType& limits,
363 const std::vector<Move>& searchMoves, StateStackPtr& states) {
364 wait_for_search_finished();
366 SearchTime = Time::now(); // As early as possible
368 Signals.stopOnPonderhit = Signals.firstRootMove = false;
369 Signals.stop = Signals.failedLowAtRoot = false;
373 SetupStates = states; // Ownership transfer here
376 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
377 if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
378 RootMoves.push_back(RootMove(ml.move()));
380 main_thread()->is_finished = false;
381 main_thread()->notify_one(); // Starts main thread